Extended Data Fig. 2: Intra-bilayer stacking disorder existing only on the surface.

a, b, The snapshots of MD simulations of intra-bilayer stacking disorder on the topmost surface. The hexagonal surface bilayer was grown on an Ih substrate after an equilibration period of 2500 ns. To see more clearly, we extracted two 12 nm × 12 nm images from the original calculated image. Typical “55-8-55” line defects between the Ic and Ih domains at the surface are denoted by blue dashed lines. It should be mentioned that the mW potential does not explicitly include the individual H atoms. O atoms in the topmost bilayer and the bulk are denoted as red and light blue spheres, respectively. c, The evolution of the second topmost bilayer after the deposition of a new surface bilayer. Water molecules with cubic and hexagonal ice order are identified using CHILL +⁶¹ and the cubicity is defined as the ratio of the number of Ic-stacking water molecules to the total number of molecules in both Ic and Ih-stacking patterns within the second topmost bilayer. Upon deposition of a new bilayer and subsequent equilibration at 180 K, there is a gradual decrease in the area of Ic-stacking nanodomains that existed in the previously deposited bilayer (now the second topmost bilayer) with time (Supplementary Video 1). Consequently, this clearly indicates that the intra-bilayer stacking disorder only exists on the surface.